Multi-layer biaxially oriented polymer film

ABSTRACT

A multi-layer biaxially oriented polymer film comprising a core layer (CL) and at least one sealing layer (SL), said sealing layer(s) (SL) comprise(s) a propylene copolymer composition (P) having a comonomer content in the range of 3.0 to 8.0 wt.-%, the comonomers are C5 to C12 α-olefins, said propylene copolymer composition (P) comprises a polypropylene (A) and a polypropylene (B) in the weight ratio [(A)/(B)] of 20/80 to 80/20, wherein said polypropylene (A) has a comonomer content of equal or below 4.0 wt.-%, the comonomers are C5 to C12 α-olefins, and said propylene copolymer (B) has a comonomer content of 4.0 to 20.0 wt.-%, the comonomers are C5 to C12 α-olefins.

The present invention is directed to a new multi-layer biaxiallyoriented polymer film comprising at least one sealing layer with goodoptical and sealing properties, as well as to its manufacture.

Polypropylenes are suitable for many applications. For instancepolypropylene is applicable in areas where sealing properties play animportant role, like in the food packing industry. Irrespectively fromthe polymer type, a polymer must fulfill at best all desired endproperties and additionally must be easily processable, i.e. mustwithstand stress. However end properties and processing properties actoften in a conflicting manner.

In many cases, the seal which is formed between the surfaces to besealed is put under load while it is still warm. This means that thehot-tack properties of the polypropylene are crucial to ensure that astrong seal is formed even before cooling. But not only the hot tackstrength should be rather high but also the heat sealing initiationtemperature should be rather low. By operating at lower temperaturethere is the benefit that the article to be sealed is not exposed tohigh temperature. There are also economic advantages since lowertemperatures are of course cheaper to generate and maintain. Further,all extrusion products have a window within which sealing may occur,i.e. in which the sealing layer becomes partly molten. Traditionallythis sealing window has been rather narrow meaning that temperaturecontrol during the heat sealing process is critical. Accordingly a broadsealing window would be appreciated because in such a case thetemperature control during heat sealing is less important.

Finally for many applications the multi-layer biaxially oriented polymerfilm shall also have good optical properties.

Accordingly the object of the present invention is to provide a materialenabling a skilled person to produce a multi-layer biaxially orientedpolymer film having high hot tack strength, low heat sealing initiationtemperature (SIT), broad processing window, low stickiness and goodoptical properties.

The finding of the present invention is to provide a multi-layerbiaxially oriented polymer film comprising a core layer (CL) being apolypropylene (PP), preferably a propylene homopolymer (H-PP), and asealing layer (SL) comprising a propylene copolymer composition (P) withrather high comonomer content, the comonomers are long chain α-olefins,and said propylene copolymer composition (P) comprises two differentfractions, said fractions differ in the comonomer content.

Accordingly in a first embodiment the present invention is directed to amulti-layer biaxially oriented polymer film comprising

-   (a) a core layer (CL) being selected from the group consisting of    polyvinyl alcohols, polyacrylates, polyamides, poly(ethylene    terephthalate), polyolefins (PO) and mixtures thereof, and-   (b) a sealing layer (SL),    said sealing layer (SL) comprises a propylene copolymer composition    (P), said propylene copolymer composition (P)-   (c1) has a comonomer content in the range of 3.0 to 8.0 wt.-%, the    comonomers are C₅ to C₁₂ α-olefins,-   (c2) comprises a polypropylene (A) and a polypropylene (B) in the    weight ratio [(A)/(B)] of 20/80 to 80/20, preferably of 25/75 to    75/25, more preferably of 30/70 to 70/30, still more preferably of    35/65 to 50/50,    wherein    -   said polypropylene (A) has a comonomer content of equal or below        4.0 wt.-%, the comonomers are C₅ to C₁₂ α-olefins, and    -   said propylene copolymer (B) has a comonomer content of 4.0 to        20.0 wt.-%, the comonomers are C₅ to C₁₂ α-olefins.

Alternatively (second embodiment) the present invention can be definedas a multi-layer biaxially oriented polymer film comprising

-   (a) a core layer (CL) being selected from the group consisting of    polyvinyl alcohols, polyacrylates, polyamides, poly(ethylene    terephthalate), polyolefins (PO) and mixtures thereof, and-   (b) a sealing layer (SL),    said sealing layer (SL) comprises a propylene copolymer composition    (P), said propylene copolymer composition (P) has-   (c1) a comonomer content in the range of 3.0 to 8.0 wt.-%, the    comonomers are C₅ to C₁₂ α-olefins,-   (c2) a melting temperature Tm determined by differential scanning    calorimetry (DSC) of at least 135° C., and-   (c3) a heat sealing initiation temperature (SIT) of equal or below    112° C., preferably of equal or below 110° C.

It has surprisingly been found that a multi-layer biaxially orientedpolymer film according to the first or second embodiment has a low heatsealing initiation temperature (SIT), a broad sealing window, a high hottack strength and good optical properties (see example section).

In the following the two embodiments are defined in more detailtogether.

The multi-layer biaxially oriented polymer film has preferably drawratio in machine direction and transverse direction of 1.5 to 9, such asfrom 2 to 8, preferably 2.5 to 8.

The multi-layer biaxially oriented polymer film according to the instantinvention comprises a core layer (CL) and at least one sealing layer(SL). Accordingly the multi-layer biaxially oriented polymer film maycomprise additional layers like an outer layer (OL) and/or a metal layer(ML), the latter is preferred. The metal layer (ML) is applied after thepolymer layers, in particular the core layer (CL), the sealing layers(SL) and optionally the outer layer (OL) have been biaxially oriented.

In one preferred embodiment the multi-layer biaxially oriented polymerfilm comprises at least three layers, namely at least one core layer(CL), and two sealing layers (SL), namely a first sealing layer (SL) anda second sealing layer (SL), wherein the multi-layer biaxially orientedpolymer film has the stacking order first sealing layer (SL)-core layer(CL)-second sealing layer (SL). Accordingly in one preferred embodimentthe (two) sealing layer(s) are directly co-extruded with the core layer(CL) and subsequently biaxially stretched. Thus in one specificpreferred embodiment the multi-layer biaxially oriented polymer filmconsists of two sealing layers (SL) and one core layer (CL) having thestacking order first sealing layer (SL)-core layer (CL)-second sealinglayer (SL). The first sealing layer (SL) and second sealing layer (SL)can be chemically different or identical, the latter being preferred.

In another preferred embodiment the multi-layer biaxially orientedpolymer film comprises at least three layers, namely a core layer (CL),a sealing layer (SL) and a metal layer (ML), wherein the sealing layer(SL) is located, i.e. joined, on the one side (surface) of the corelayer (CL) and the metal layer (ML) is located, i.e. joined, on theother side (surface) of the core layer (CL). Accordingly the multi-layerbiaxially oriented polymer film has the stacking order sealing layer(SL)-core layer (CL)-metal layer (ML). Preferably the sealing layer (SL)is co-extruded with the core layer (CL), biaxially stretched andsubsequently the core layer (CL) is metallized obtaining the metal layer(ML).

In another preferred embodiment the multi-layer biaxially orientedpolymer film comprises at least three layers, namely a core layer (CL),a sealing layer (SL) and a outer layer (OL), wherein the sealing layer(SL) is located, i.e. joined, on the one side (surface) of the corelayer (CL) and the outer layer (OL) is located, i.e. joined, on theother side (surface) of the core layer (CL). Accordingly the multi-layerbiaxially oriented polymer film has the stacking order sealing layer(SL)-core layer (CL)-outer layer (OL). In one embodiment the sealinglayer (SL) and the outer layer (OL) are co-extruded with the core layer(CL) and subsequently biaxially stretched.

The thickness of the core layer (CL) is preferably in the range of 5 to80 μm, more preferably in the range of 10 to 50 μm.

Preferably the sealing layer(s) (SL) has/have a thickness that issubstantially less than the thickness of the core layer (CL) andsubstantially less than the thickness of the total multi-layer biaxiallyoriented polymer film. In one embodiment the thickness of the sealinglayer(s) (SL) is/are substantially less, usually less than 20%, of thethickness of the core layer (CL). Accordingly it is appreciated that thesealing layer(s) (SL) has/have a thickness in the range of 0.2 to 15 μm,more preferably in the range of 0.5 to 10 μm.

The outer layer (OL)—if present—may have a thickness in the range of 0.5to 50 μm, more preferably in the range of 0.7 to 20 μm.

Preferably the multi-layer biaxially oriented polymer film is obtainedby coextrusion. The extrusion coating can be accomplished on a blownfilm line or on a cast film line, the latter being preferred. Aftercoextrusion the multi-layer biaxially oriented polymer film is biaxiallystretched. In case of the blown film line stretching is accomplished bya second bubble forming A preferred process for the preparation of amulti-layer biaxially oriented polymer film according to this inventionis described in more detail below.

As used herein, the phrase “core layer” although singular, may refer toone or more layers, like to 2 to 5 layers, i.e. 2, 3, 4, or 5 layers,that form the core of the multi-layer biaxially oriented polymer film.The core layer (CL) will typically be formed from a polymer selectedfrom the group consisting of polyvinyl alcohol, polyacrylate, polyamide,polyester, like poly(ethylene terephthalate), polyolefin (PO) andmixtures thereof having desired properties or characteristics, such asgood stiffness or barrier properties. Accordingly it is in particularpreferred that the core layer (CL) is a polyolefin (PO), more preferablya polyethylene (PE) or polypropylene (PP), still more preferably apropylene copolymer (C-PP) or a propylene homopolymer (H-PP), the latterbeing preferred. In case of a propylene copolymer, said copolymer haspreferably a comonomer content between 0.1 and 5 wt.-%, the comonomersare ethylene and/or C₄ to C₈ α-olefins, preferably ethylene, 1-butene or1-hexene.

In one preferred embodiment the polypropylene (PP), preferably thepropylene homopolymer (H-PP), of the core layer (CL) has a melt flowrate MFR₂ (230° C.) measured according to ISO 1133 in the range of 1.0to 15.0 g/10 min, more preferably in the range of 1.0 to 10.0 g/10 min.

The melting temperature Tm determined by differential scanningcalorimetry (DSC) of the polypropylene (PP), more preferably of thepropylene homopolymer (H-PP), is at least 150° C., preferably at least155° C., more preferably in the range of 150 to 166° C., like in therange of 160 to 164° C.

The outer layer (OL)—if present—is preferably a polyolefin (PO). Thepolyolefin (PO) of the outer layer (OL) can be identical or different tothe polyolefin (PO) of the core layer (CL). Accordingly with regard tothe preferred polyolefin (PO) used as the outer layer (OL) reference ismade to the information provided above for the polyolefin (PO) used asthe core layer (CL). In one embodiment the outer layer (OL) is apolyamide, a polyester, a polyvinyl alcohol, a polyethylene (PE) or apolypropylene (PP).

As a further requirement the sealing layer(s) (SL) of the multi-layerbiaxially oriented polymer film must comprise a propylene copolymercomposition (P). In a preferred embodiment the sealing layer(s) (SL)comprise(s) the propylene copolymer composition (P) as the only polymercomponent. Accordingly it is preferred that the amount of the propylenecopolymer composition (P) within the sealing layer(s) (SL) is at least70 wt.-%, more preferably at least 80 wt.-%, still more preferably atleast 90 wt.-%, still yet more preferably at least 95 wt.-%, like atleast 99 wt.-%. In one preferred embodiment the sealing layer(s) (SL)consist(s) of the propylene copolymer composition (P).

The propylene copolymer composition (P) according to this invention isfeatured by a rather high comonomer content. A “comonomer” according tothis invention is a polymerizable unit different to propylene.Accordingly the propylene copolymer composition (P) according to thisinvention shall have a comonomer content of at least 2.5 wt.-%, morepreferably of at least 3.0 wt.-%, more preferably of at least 3.3 wt.-%,still more preferably of at least 3.5 wt.-%, like of at least 3.8 wt.-%.Thus it is preferred that the propylene copolymer composition (P)according to this invention has a comonomer content in the range of 2.0to 10.0 wt.-%, more preferably in the range of 3.0 to 8.0 wt.-%, stillmore preferably in the range of 3.2 to 7.5 wt.-%, still more preferablyin the range of 3.3 to 7.5 wt.-%, like in the range of 3.5 to 6.5 wt.-%.

In a preferred embodiment the amount of comonomer within the sealinglayer(s) (SL) is the same as for the propylene copolymer composition(P).

The comonomers of the propylene copolymer composition (P) are C₅ to C₁₂α-olefins, e.g. 1-hexene and/or 1-octene. The propylene copolymercomposition (P) of the present invention may contain more than one typeof comonomer. Thus the propylene copolymer composition (P) of thepresent invention may contain one, two or three different comonomers,the comonomers are selected from the group of C₅ α-olefin, C₆ α-olefin,C₇ α-olefin, C₈ α-olefin, C₉ α-olefin, C₁₀ α-olefin, C₁₁ α-olefin, andC₁₂ α-olefin. However it is preferred that the propylene copolymercomposition (P) contains only one type of comonomer. Preferably thepropylene copolymer composition (P) comprises—apart from propylene—only1-hexene and/or 1-octene. In an especially preferred embodiment thecomonomer of the propylene copolymer composition (P) is only 1-hexene.

The propylene copolymer composition (P) as well as the propylenecopolymer (B) and the propylene copolymer (C-A) according to thisinvention are preferably random propylene copolymers. The term “randomcopolymer” has to be preferably understood according to IUPAC (PureAppl. Chem., Vol. No. 68, 8, pp. 1591 to 1595, 1996). Preferably themolar concentration of comonomer dyads, like 1-hexene dyads, obeys therelationship[HH]<[H] ²wherein[HH] is the molar fraction of adjacent comonomer units, like of adjacent1-hexene units, and[H] is the molar fraction of total comonomer units, like of total1-hexene units, in the polymer.

Preferably the propylene copolymer composition (P) as well as thepropylene copolymer (C-A) and the propylene copolymer (B) as defined indetail below are isotactic. Accordingly it is appreciated that thepropylene copolymer composition (P), the propylene copolymer (C-A) andthe propylene copolymer (B) have a rather high isotactic triadconcentration, i.e. higher than 90%, more preferably higher than 92%,still more preferably higher than 93% and yet more preferably higherthan 95%, like higher than 97%.

The molecular weight distribution (MWD) is the relation between thenumbers of molecules in a polymer and the individual chain length. Themolecular weight distribution (MWD) is expressed as the ratio of weightaverage molecular weight (M_(w)) and number average molecular weight(M_(n)). The number average molecular weight (M_(n)) is an averagemolecular weight of a polymer expressed as the first moment of a plot ofthe number of molecules in each molecular weight range against themolecular weight. In effect, this is the total molecular weight of allmolecules divided by the number of molecules. In turn, the weightaverage molecular weight (M_(w)) is the first moment of a plot of theweight of polymer in each molecular weight range against molecularweight.

The number average molecular weight (M_(n)) and the weight averagemolecular weight (M_(w)) as well as the molecular weight distribution(MWD) are determined by size exclusion chromatography (SEC) using WatersAlliance GPCV 2000 instrument with online viscometer. The oventemperature is 140° C. Trichlorobenzene is used as a solvent (ISO16014).

Accordingly it is preferred that the inventive propylene copolymercomposition (P) has a weight average molecular weight (M_(w)) from 100to 700 kg/mol, more preferably from 150 to 400 kg/mol.

The number average molecular weight (M_(n)) of the polypropylene ispreferably in the range of 25 to 200 kg/mol, more preferably from 30 to150 kg/mol.

Further it is appreciated that the molecular weight distribution (MWD)measured according to ISO 16014 is at least 2.5, preferably at least 3,more preferably in the range of 2.5 to 8, more preferably 3 to 5.

Furthermore, it is preferred that the propylene copolymer composition(P) of the present invention has a melt flow rate (MFR) given in aspecific range. The melt flow rate measured under a load of 2.16 kg at230° C. (ISO 1133) is denoted as MFR₂. Accordingly, it is preferred thatin the present invention the propylene copolymer composition (P) has amelt flow rate MFR₂ measured according to ISO 1133 in the range of 2.0to 50.0 g/10 min, more preferably in the range of 3.0 to 25.0 g/10 min,still more preferably in the range of 3.0 to 20.0 g/10 min, yet stillmore preferably in the range of 4.0 to 15.0 g/10 min.

In a preferred embodiment the molecular weight distribution (MWD), theweight average molecular weight (M_(w)), the number average molecularweight (M_(n)) and the melt flow rate (MFR) of the sealing layer(s) (SL)is the same as for the propylene copolymer composition (P) indicatedabove.

As mentioned above, the multi-layer biaxially oriented polymer filmshall be especially suitable for the packing industry. Accordingly goodsealing properties are desired, like rather low heat sealing initiationtemperature (SIT) and low stickiness.

Accordingly it is preferred that the sealing layer(s) (SL) and thus alsothe propylene copolymer composition (P) has/have a heat sealinginitiation temperature (SIT) of not more than 115° C., more preferablyof equal or below 110° C., still more preferably in the range of 90 to115° C., yet more preferably in the range of 93 to equal or below 110°C.

Alternatively or additionally the multi-layer biaxially oriented polymerfilm has a heat sealing initiation temperature (SIT) of not more than115° C., more preferably of equal or below 110° C., still morepreferably in the range of 90 to 115° C., yet more preferably in therange of 93 to equal or below 110° C.

But not only the heat sealing initiation temperature (SIT) shall berather low but also the melting temperature (T_(m)) shall be ratherhigh. Accordingly the difference between the melting temperature (T_(m))and the heat sealing initiation temperature (SIT) shall be rather high.Thus it is preferred that the sealing layer(s) (SL) and/or the propylenecopolymer composition (P) fulfill(s) the equation (I), more preferablythe equation (Ia), still more preferably the equation (Ib),Tm−SIT≥22° C.  (I)Tm−SIT≥24° C.  (Ia)Tm−SIT≥27° C.  (Ib)wherein

-   Tm is the melting temperature given in centigrade [° C.] of the    sealing layer(s) (SL) and/or of the propylene copolymer composition    (P),-   SIT is the heat sealing initiation temperature (SIT) given in    centigrade [° C.] of the sealing layer(s) (SL) and/or of the    propylene copolymer composition (P).

The melting temperature (T_(m)) measured according to ISO 11357-3 of thesealing layer(s) (SL) and/or of the propylene copolymer composition (P)is preferably at least 125.0° C., more preferably of at least 128° C.,still more preferably of at least 135° C., like at least 140° C. Thus itis in particular appreciated that the melting temperature (T_(m))measured according to ISO 11357-3 of the sealing layer(s) (SL) and/or ofthe propylene copolymer composition (P) is in the range of 125 to 155°C., more preferably in the range of 128 to 150° C., still morepreferably in the range of 135 to 155° C., still yet more preferably inthe range of 135 to 150° C., like in the range of 140 to 150° C.

Additionally it is appreciated that the sealing layer(s) (SL) and/or thepropylene copolymer composition (P) of the instant invention has/have acrystallization temperature (TO measured according to ISO 11357-3 of atleast 88° C., more preferably of at least 90° C. Accordingly the sealinglayer(s) (SL) and/or the propylene copolymer composition (P) has/havepreferably a crystallization temperature (TO measured according to ISO11357-3 in the range of 88 to 115° C., more preferably in the range of90 to 112° C.

Additionally the sealing layer(s) (SL) and/or the propylene copolymercomposition (P) can be defined by the xylene cold soluble (XCS) content.Accordingly the sealing layer(s) (SL) and/or the propylene copolymercomposition (P) is/are preferably featured by a xylene cold soluble(XCS) content of below 25.0 wt.-%, more preferably of below 22.0 wt.-%,yet more preferably equal or below 20.0 wt.-%, still more preferablybelow 16.0 wt.-%. Thus it is in particular appreciated that the sealinglayer(s) (SL) and/or the propylene copolymer composition (P) of theinstant invention has/have a xylene cold soluble (XCS) content in therange of 0.5 to 25.0 wt.-%, more preferably in the range of 0.5 to 20.0wt.-%, yet more preferably in the range of 0.5 to 16.0 wt.-%.

The amount of xylene cold soluble (XCS) additionally indicates that thesealing layer(s) (SL) and/or the propylene copolymer composition (P)is/are preferably free of any elastomeric polymer component, like anethylene propylene rubber. In other words the sealing layer(s) (SL)and/or the propylene copolymer composition (P) shall be not aheterophasic polypropylene, i.e. a system consisting of a polypropylenematrix in which an elastomeric phase is dispersed. Such systems arefeatured by a rather high xylene cold soluble content. Accordingly in apreferred embodiment the propylene copolymer composition (P) comprisesthe polypropylene (A) and the propylene copolymer (B) as the onlypolymer components.

Similar to xylene cold solubles (XCS) the hexane hot soluble (HHS)indicate that part of a polymer which has a low isotacticity andcrystallinity and which is soluble in hexane at 50° C.

Accordingly it is preferred that the sealing layer(s) (SL) and/or thepropylene copolymer composition (P) has/have hexane hot solubles (HHS)measured according to FDA 177.1520 of not more than 2.5 wt.-%, morepreferably not more than 2.0 wt.-%, like not more than 1.5 wt.-%.

The propylene copolymer composition (P) of the present invention isfurther defined by its polymer fractions present. Accordingly thepropylene copolymer composition (P) of the present invention comprisesat least, preferably consists of, two fractions, namely thepolypropylene (A) and the propylene copolymer (B). Further thepolypropylene (A) is preferably the comonomer lean fraction whereas thepropylene copolymer (B) is the comonomer rich fraction.

Thus it is appreciated that the polypropylene (A) has a comonomercontent of equal or below 5.0 wt.-%, more preferably of equal or below4.0 wt.-%. Accordingly the polypropylene (A) can be a propylenehomopolymer (H-A) or a propylene copolymer (C-A).

The expression homopolymer used in the instant invention relates to apolypropylene that consists of at least 99.5 wt.-%, more preferably ofat least 99.8 wt.-%, of propylene units. In a preferred embodiment onlypropylene units in the propylene homopolymer are detectable.

In case the polypropylene (A) is a propylene copolymer (C-A) thecomonomer content is in the range of 0.2 to equal or below 5.0 wt.-%,preferably in the range 0.5 to equal or below 4.0 wt.-%. More preferablythe propylene copolymer (C-A) is a random propylene copolymer. Thecomonomers of the propylene copolymer (C-A) are C₅ to C₁₂ α-olefins,more preferably the comonomers of the propylene copolymer (C-A) areselected from the group of C₅ α-olefin, C₆ α-olefin, C₇ α-olefin, C₈α-olefin, C₉ α-olefin, C₁₀ α-olefin, C₁₁ α-olefin, an C₁₂ α-olefin,still more preferably the comonomers of the propylene copolymer (C-A)are 1-hexene and/or 1-octene. The propylene copolymer (C-A) may containmore than one type of comonomer. Thus the propylene copolymer (C-A) ofthe present invention may contain one, two or three differentcomonomers. However it is preferred that the propylene copolymer (C-A)contains only one type of comonomer. Preferably the propylene copolymer(C-A) comprises—apart from propylene—only 1-hexene and/or 1-octene. Inan especially preferred embodiment the comonomer of the propylenecopolymer (C-A) is only 1-hexene.

Thus the propylene copolymer (C-A) is in one preferred embodiment apropylene copolymer of propylene and 1-hexene only, wherein the 1-hexenecontent is in the range of 0.2 to 5.0 wt-%, preferably in the range of0.5 to equal or below 4.0 wt-%.

The propylene copolymer (B) has preferably a higher comonomer contentthan the polypropylene (A). Accordingly the propylene copolymer (B) hasa comonomer content of equal or more than 2.5 wt.-% to 20.0 wt.-%, morepreferably of equal or more than 3.0 to 15.0 wt.-%, still morepreferably of equal or more than 4.0 to 12.0 wt.-%.

More preferably the propylene copolymer (B) is a random propylenecopolymer.

The comonomers of the propylene copolymer (B) are C₅ to C₁₂ α-olefins,more preferably the comonomers of the propylene copolymer (B) areselected from the group of C₅ α-olefin, C₆ α-olefin, C₇ α-olefin, C₈α-olefin, C₉ α-olefin, C₁₀ α-olefin, C₁₁ α-olefin, an C₁₂ α-olefin,still more preferably the comonomers of the propylene copolymer (B) are1-hexene and/or 1-octene. The propylene copolymer (B) may contain morethan one type of comonomer. Thus the propylene copolymer (B) of thepresent invention may contain one, two or three different comonomers.However it is preferred that the propylene copolymer (B) contains onlyone type of comonomer. Preferably the propylene copolymer (B)comprises—apart from propylene—only 1-hexene and/or 1-octene. In anespecially preferred embodiment the comonomer of the propylene copolymer(B) is only 1-hexene.

Thus the propylene copolymer (B) is in a preferred embodiment apropylene copolymer of propylene and 1-hexene only, wherein the 1-hexenecontent is in the range of equal or more than 2.5 wt.-% to 20.0 wt.-%,more preferably of equal or more than 3.0 to 15.0 wt.-%, still morepreferably of equal or more than 4.0 to 12.0 wt.-%.

It is in particular preferred that the comonomers of the propylenecopolymer (C-A) and of the propylene copolymer (B) are the same.Accordingly in one preferred embodiment the propylene copolymercomposition (P) of the instant invention comprises, preferably comprisesonly, a propylene copolymer (C-A) and a propylene copolymer (B), in bothpolymers the comonomer is only 1-hexene.

In another preferred embodiment the propylene copolymer composition (P)of the instant invention comprises, preferably comprises only, apropylene homopolymer (H-A) and a propylene copolymer (B), wherein thecomonomers of the propylene copolymer (B) are selected from the groupconsisting of C₅ α-olefin, C₆ α-olefin, C₇ α-olefin, C₈ α-olefin, C₉α-olefin, C₁₀ α-olefin, C₁₁ α-olefin, an C₁₂ α-olefin, preferably thecomonomers of the propylene copolymer (B) are 1-hexene and/or 1-octene,more preferably the comonomer of the propylene copolymer (B) is 1-hexeneonly.

As mentioned above polypropylene (A) is preferably the comonomer leanfraction whereas the propylene copolymer (B) is the comonomer richfraction. Accordingly the comonomer content in the polypropylene (A) islower compared to the comonomer content of the propylene copolymer (B).Thus it is appreciated that the propylene copolymer composition (P) andthe polypropylene (A) fulfil together the correlation [com (P)−com (A)]being at least 1.0, i.e. in the range of 1.0 to 6.0, more preferablybeing in the range of 1.0 to 4.5, still more preferably in the range of1.5 to 4.0,

wherein

-   com (A) is the comonomer content of the polypropylene (A) given in    weight percent [wt.-%],-   com (P) is the comonomer content of the propylene copolymer    composition (P) given in weight percent [wt.-%].

One important aspect of the present invention is that the polypropylene(A) and the propylene copolymer (B) of the propylene copolymercomposition (P) differ in the comonomer content. Additionally thepolypropylene (A) and the propylene copolymer (B) of the propylenecopolymer composition (P) may also differ in the melt flow rate.Accordingly the ratio MFR (A)/MFR (P) is equal or below 1.0, morepreferably equal or below 0.70, yet more preferably equal or below 0.60,still more preferably equal or below 0.55,

wherein

-   MFR (A) is the melt flow rate MFR₂ (230° C.) [g/10 min] measured    according to ISO 1133 of the polypropylene (A),-   MFR (P) is the melt flow rate MFR₂ (230° C.) [g/10 min] measured    according to ISO 1133 of the propylene copolymer composition (P).

Further it is appreciated that the polypropylene (A) has a melt flowrate MFR₂ (230° C.) measured according to ISO 1133 of at least 0.5 g/10min, more preferably of at least 1.5 g/10 min, still more preferably inthe range of 1.0 to 8.0 g/10 min, still more preferably in the range of1.5 to 7.0 g/10 min, yet more preferably in the range of 2.0 to 5.0 g/10min, like in the range of 2.5 to 5.0 g/10 min.

As a high melt flow rate indicates a low molecular weight, it isappreciated that the polypropylene (A) has a weight average molecularweight (M_(w)) of below 450 kg/mol, still more preferably of below 400kg/mol, yet more preferably in the range of 150 to below 450 kg/mol,like in the range of 180 to 400 kg/mol.

Further the polypropylene (A) has preferably a xylene cold soluble (XCS)content of below 2.5 wt.-%, more preferably of below 2.0 wt.-%, stillmore preferably in the range of 0.3 to 2.5 wt.-%, yet more preferably inthe range of 0.3 to 2.0 wt.-%. It is in particular preferred that thepropylene copolymer (A) has a lower xylene cold soluble (XCS) contentthan the propylene copolymer (B).

The propylene copolymer composition (P) may contain additives known inthe art, like antioxidants, nucleating agents, slip agents andantistatic agents. The polymer fraction, preferably the sum of thepolypropylene (A) and the propylene copolymer (B) fractions, is at least90 wt.-%, more preferably at least 95 wt.-%, still more preferably atleast 98 wt.-%, like at least 99 wt.-%.

In the following the preparation of the multi-layer biaxially orientedpolymer film is defined in more detail.

The polymers used for the core layer (CL) are known in the art and arenot on focus in this invention. Typical commercially available polyvinylalcohols, polyacrylates, polyamides, polyolefins (PO), like propylenehomopolymer (H-PP), can be used for the core layer (CL).

The propylene copolymer composition (P) is preferably obtained by asequential polymerization process comprising at least two reactorsconnected in series, wherein said process comprises the steps of

-   (A) polymerizing in a first reactor (R-1) being a slurry reactor    (SR), preferably a loop reactor (LR), propylene and optionally at    least one C₅ to C₁₂ α-olefin, preferably 1-hexene, obtaining a    polypropylene (A) as defined in the instant invention,-   (B) transferring said polypropylene (A) and unreacted comonomers of    the first reactor in a second reactor (R-2) being a gas phase    reactor (GPR-1),-   (C) feeding to said second reactor (R-2) propylene and at least one    C₅ to C₁₂ α-olefin,-   (D) polymerizing in said second reactor (R-2) and in the presence of    said first polypropylene (A) propylene and at least one C₅ to C₁₂    α-olefin obtaining a propylene copolymer (B) as defined in the    instant invention, said polypropylene (A) and said propylene    copolymer (B) form the propylene copolymer composition (P) as    defined in the instant invention,    wherein further    in the first reactor (R-1) and second reactor (R-2) the    polymerization takes place in the presence of a solid catalyst    system (SCS), said solid catalyst system (SCS) comprises-   (i) a transition metal compound of formula (I)    R _(n)(Cp′)₂ MX ₂  (I)    -   wherein    -   “M” is zirconium (Zr) or hafnium (Hf),    -   each “X” is independently a monovalent anionic σ-ligand,    -   each “Cp′” is a cyclopentadienyl-type organic ligand        independently selected from the group consisting of substituted        cyclopentadienyl, substituted indenyl, substituted        tetrahydroindenyl, and substituted or unsubstituted fluorenyl,        said organic ligands coordinate to the transition metal (M),    -   “R” is a bivalent bridging group linking said organic ligands        (Cp′),    -   “n” is 1 or 2, preferably 1, and-   (ii) optionally a cocatalyst (Co) comprising an element (E) of group    13 of the periodic table (IUPAC), preferably a cocatalyst (Co)    comprising a compound of Al.

Concerning the definition of the propylene copolymer composition (P),the polypropylene (A) and the propylene copolymer (B) it is referred tothe definitions given above.

The term “sequential polymerization process” indicates that thepropylene copolymer composition (P) is produced in at least two reactorsconnected in series. Accordingly, a decisive aspect of the presentprocess is the preparation of the propylene copolymer composition (P) intwo different reactors. Thus the present process comprises at least afirst reactor (R-1) and a second reactor (R-2). In one specificembodiment the instant process consists of two polymerization reactors(R-1) and (R-2). The term “polymerization reactor” shall indicate thatthe main polymerization takes place. Thus in case the process consistsof two polymerization reactors, this definition does not exclude theoption that the overall process comprises for instance apre-polymerization step in a pre-polymerization reactor. The term“consists of” is only a closing formulation in view of the mainpolymerization reactors.

The first reactor (R-1) is preferably a slurry reactor (SR) and can beany continuous or simple stirred batch tank reactor or loop reactoroperating in bulk or slurry. Bulk means a polymerization in a reactionmedium that comprises of at least 60% (wt/wt), preferably 100% monomer.According to the present invention the slurry reactor (SR) is preferablya (bulk) loop reactor (LR).

The second reactor (R-2) and any subsequent reactor are preferably gasphase reactors (GPR). Such gas phase reactors (GPR) can be anymechanically mixed or fluid bed reactors. Preferably the gas phasereactors (GPR) comprise a mechanically agitated fluid bed reactor withgas velocities of at least 0.2 msec. Thus it is appreciated that the gasphase reactor is a fluidized bed type reactor preferably with amechanical stirrer.

The condition (temperature, pressure, reaction time, monomer feed) ineach reactor is dependent on the desired product which is in theknowledge of a person skilled in the art. As already indicated above,the first reactor (R-1) is preferably a slurry reactor (SR), like a loopreactor (LR), whereas the second reactor (R-2) is preferably a gas phasereactor (GPR-1). The subsequent reactors—if present—are also preferablygas phase reactors (GPR).

A preferred multistage process is a “loop-gas phase”-process, such asdeveloped by Borealis A/S, Denmark (known as BORSTAR® technology)described e.g. in patent literature, such as in EP 0 887 379 or in WO92/12182.

Multimodal polymers can be produced according to several processes whichare described, e.g. in WO 92/12182, EP 0 887 379, and WO 98/58976. Thecontents of these documents are included herein by reference.

Preferably, in the instant process for producing propylene copolymercomposition (P) as defined above the conditions for the first reactor(R−1), i.e. the slurry reactor (SR), like a loop reactor (LR), of step(A) may be as follows:

-   -   the temperature is within the range of 40° C. to 110° C.,        preferably between 60° C. and 100° C., 70 to 90° C.,    -   the pressure is within the range of 20 bar to 80 bar, preferably        between 40 bar to 70 bar,    -   hydrogen can be added for controlling the molar mass in a manner        known per se.

Subsequently, the reaction mixture from step (A) is transferred to thesecond reactor (R-2), i.e. gas phase reactor (GPR-1), i.e. to step (D),whereby the conditions in step (D) are preferably as follows:

-   -   the temperature is within the range of 50° C. to 130° C.,        preferably between 60° C. and 100° C.,    -   the pressure is within the range of 5 bar to 50 bar, preferably        between 15 bar to 40 bar,    -   hydrogen can be added for controlling the molar mass in a manner        known per se.

The residence time can vary in both reactor zones.

In one embodiment of the process for producing propylene copolymercomposition (P) the residence time in bulk reactor, e.g. loop is in therange 0.2 to 4 hours, e.g. 0.3 to 1.5 hours and the residence time ingas phase reactor will generally be 0.2 to 6.0 hours, like 0.5 to 4.0hours.

If desired, the polymerization may be effected in a known manner undersupercritical conditions in the first reactor (R-1), i.e. in the slurryreactor (SR), like in the loop reactor (LR), and/or as a condensed modein the gas phase reactor (GPR-1).

The conditions in the other gas phase reactors (GPR), if present, aresimilar to the second reactor (R-2).

The present process may also encompass a pre-polymerization prior to thepolymerization in the first reactor (R-1). The pre-polymerization can beconducted in the first reactor (R-1), however it is preferred that thepre-polymerization takes place in a separate reactor, so calledpre-polymerization reactor.

In one specific embodiment the solid catalyst system (SCS) has aporosity measured according ASTM 4641 of less than 1.40 ml/g and/or asurface area measured according to ASTM D 3663 of lower than 25 m²/g.

Preferably the solid catalyst system (SCS) has a surface area of lowerthan 15 m²/g, yet still lower than 10 m²/g and most preferred lower than5 m²/g, which is the lowest measurement limit. The surface areaaccording to this invention is measured according to ASTM D 3663 (N₂).

Alternatively or additionally it is appreciated that the solid catalystsystem (SCS) has a porosity of less than 1.30 ml/g and more preferablyless than 1.00 ml/g. The porosity has been measured according to ASTM4641 (N₂). In another preferred embodiment the porosity is notdetectable when determined with the method applied according to ASTM4641 (N₂).

Furthermore the solid catalyst system (SCS) typically has a meanparticle size of not more than 500 μm, i.e. preferably in the range of 2to 500 μm, more preferably 5 to 200 μm. It is in particular preferredthat the mean particle size is below 80 μm, still more preferably below70 μm. A preferred range for the mean particle size is 5 to 70 μm, oreven 10 to 60 μm.

As stated above the transition metal (M) is zirconium (Zr) or hafnium(Hf), preferably zirconium (Zr).

The term “σ-ligand” is understood in the whole description in a knownmanner, i.e. a group bound to the metal via a sigma bond. Thus theanionic ligands “X” can independently be halogen or be selected from thegroup consisting of R′, OR′, SiR′₃, OSiR′₃, OSO₂CF₃, OCOR′, SR′, NR′₂ orPR′₂ group wherein R′ is independently hydrogen, a linear or branched,cyclic or acyclic, C₁ to C₂₀ alkyl, C₂ to C₂₀ alkenyl, C₂ to C₂₀alkynyl, C₃ to C₁₂ cycloalkyl, C₆ to C₂₀ aryl, C₇ to C₂₀ arylalkyl, C₇to C₂₀ alkylaryl, C₈ to C₂₀ arylalkenyl, in which the R′ group canoptionally contain one or more heteroatoms belonging to groups 14 to 16.In a preferred embodiments the anionic ligands “X” are identical andeither halogen, like Cl, or methyl or benzyl.

A preferred monovalent anionic ligand is halogen, in particular chlorine(Cl).

The substituted cyclopentadienyl-type ligand(s) may have one or moresubstituent(s) being selected from the group consisting of halogen,hydrocarbyl (e.g. C₁ to C₂₀ alkyl, C₂ to C₂₀ alkenyl, C₂ to C₂₀ alkynyl,C₃ to C₂₀ cycloalkyl, like C₁ to C₂₀ alkyl substituted C₅ to C₂₀cycloalkyl, C₆ to C₂₀ aryl, C₅ to C₂₀ cycloalkyl substituted C₁ to C₂₀alkyl wherein the cycloalkyl residue is substituted by C₁ to C₂₀ alkyl,C₇ to C₂₀ arylalkyl, C₃ to C₁₂ cycloalkyl which contains 1, 2, 3 or 4heteroatom(s) in the ring moiety, C₆ to C₂₀-heteroaryl, C₁ toC₂₀-haloalkyl, —SiR″₃, —SR″, —PR″₂ or —NR″₂, each R″ is independently ahydrogen or hydrocarbyl (e. g. C₁ to C₂₀ alkyl, C₁ to C₂₀ alkenyl, C₂ toC₂₀ alkynyl, C₃ to C₁₂ cycloalkyl, or C₆ to C₂₀ aryl) or e.g. in case of—NR″₂, the two substituents R″ can form a ring, e.g. five- orsix-membered ring, together with the nitrogen atom wherein they areattached to.

Further “R” of formula (I) is preferably a bridge of 1 to 4 atoms, suchatoms being independently carbon (C), silicon (Si), germanium (Ge) oroxygen (O) atom(s), whereby each of the bridge atoms may bearindependently substituents, such as C₁ to C₂₀-hydrocarbyl, tri(C₁ toC₂₀-alkyl)silyl, tri(C₁ to C₂₀-alkyl)siloxy and more preferably “R” is aone atom bridge like e.g. —SiR′″₂—, wherein each R′″ is independently C₁to C₂₀-alkyl, C₂ to C₂₀-alkenyl, C₂ to C₂₀-alkynyl, C₃ to C₁₂cycloalkyl, C₆ to C₂₀-aryl, alkylaryl or arylalkyl, or tri(C₁ to C₂₀alkyl)silyl-residue, such as trimethylsilyl-, or the two R′″ can be partof a ring system including the Si bridging atom.

In a preferred embodiment the transition metal compound has the formula(II)

wherein

-   M is zirconium (Zr) or hafnium (Hf), preferably zirconium (Zr),-   X are ligands with a σ-bond to the metal “M”, preferably those as    defined above for formula (I),    -   preferably chlorine (Cl) or methyl (CH₃), the former especially        preferred,-   R¹ are equal to or different from each other, preferably equal to,    and are selected from the group consisting of linear saturated C₁ to    C₂₀ alkyl, linear unsaturated C₁ to C₂₀ alkyl, branched saturated    C₁-C₂₀ alkyl, branched unsaturated C₁ to C₂₀ alkyl, C₃ to C₂₀    cycloalkyl, C₆ to C₂₀ aryl, C₇ to C₂₀ alkylaryl, and C₇ to C₂₀    arylalkyl, optionally containing one or more heteroatoms of groups    14 to 16 of the Periodic Table (IUPAC),    -   preferably are equal to or different from each other, preferably        equal to, and are C₁ to C₁₀ linear or branched hydrocarbyl, more        preferably are equal to or different from each other, preferably        equal to, and are C₁ to C₆ linear or branched alkyl,-   R² to R⁶ are equal to or different from each other and are selected    from the group consisting of hydrogen, linear saturated C₁-C₂₀    alkyl, linear unsaturated C₁-C₂₀ alkyl, branched saturated C₁-C₂₀    alkyl, branched unsaturated C₁-C₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₆-C₂₀    aryl, C₇-C₂₀ alkylaryl, and C₇-C₂₀ arylalkyl, optionally containing    one or more heteroatoms of groups 14 to 16 of the Periodic Table    (IUPAC),    -   preferably are equal to or different from each other and are C₁        to C₁₀ linear or branched hydrocarbyl, more preferably are equal        to or different from each other and are C₁ to C₆ linear or        branched alkyl,-   R⁷ and R⁸ are equal to or different from each other and selected    from the group consisting of hydrogen, linear saturated C₁ to C₂₀    alkyl, linear unsaturated C₁ to C₂₀ alkyl, branched saturated C₁ to    C₂₀ alkyl, branched unsaturated C₁ to C₂₀ alkyl, C₃ to C₂₀    cycloalkyl, C₆ to C₂₀ aryl, C₇ to C₂₀ alkylaryl, C₇ to C₂₀    arylalkyl, optionally containing one or more heteroatoms of groups    14 to 16 of the Periodic Table (IUPAC), SiR¹⁰ ₃, GeR¹⁰ ₃, OR¹⁰, SR¹⁰    and NR¹⁰ ₂,    -   wherein    -   R¹⁰ is selected from the group consisting of linear saturated        C₁-C₂₀ alkyl, linear unsaturated C₁ to C₂₀ alkyl, branched        saturated C₁ to C₂₀ alkyl, branched unsaturated C₁ to C₂₀ alkyl,        C₃ to C₂₀ cycloalkyl, C₆ to C₂₀ aryl, C₇ to C₂₀ alkylaryl, and        C₇ to C₂₀ arylalkyl, optionally containing one or more        heteroatoms of groups 14 to 16 of the Periodic Table (IUPAC),    -   and/or    -   R⁷ and R⁸ being optionally part of a C₄ to C₂₀ carbon ring        system together with the indenyl carbons to which they are        attached, preferably a C₅ ring, optionally one carbon atom can        be substituted by a nitrogen, sulfur or oxygen atom,-   R⁹ are equal to or different from each other and are selected from    the group consisting of hydrogen, linear saturated C₁ to C₂₀ alkyl,    linear unsaturated C₁ to C₂₀ alkyl, branched saturated C₁ to C₂₀    alkyl, branched unsaturated C₁ to C₂₀ alkyl, C₃ to C₂₀ cycloalkyl,    C₆ to C₂₀ aryl, C₇ to C₂₀ alkylaryl, C₇ to C₂₀ arylalkyl, OR¹⁰, and    SR¹⁰,    -   preferably R⁹ are equal to or different from each other and are        H or CH₃, wherein    -   R¹⁰ is defined as before,-   L is a bivalent group bridging the two indenyl ligands, preferably    being a C₂R¹¹ ₄ unit or a SiR¹¹ ₂ or GeR¹¹ ₂, wherein,    -   R¹¹ is selected from the group consisting of H, linear saturated        C₁ to C₂₀ alkyl, linear unsaturated C₁ to C₂₀ alkyl, branched        saturated C₁ to C₂₀ alkyl, branched unsaturated C₁ to C₂₀ alkyl,        C₃ to C₂₀ cycloalkyl, C₆ to C₂₀ aryl, C₇ to C₂₀ alkylaryl or C₇        to C₂₀ arylalkyl, optionally containing one or more heteroatoms        of groups 14 to 16 of the Periodic Table (IUPAC),    -   preferably Si(CH₃)₂, SiCH₃C₆H₁₁, or SiPh₂,    -   wherein C₆H₁₁ is cyclohexyl.

Preferably the transition metal compound of formula (II) is C₂-symmetricor pseudo-C₂-symmetric. Concerning the definition of symmetry it isreferred to Resconi et al. Chemical Reviews, 2000, Vol. 100, No. 4 1263and references herein cited.

Preferably the residues R¹ are equal to or different from each other,more preferably equal, and are selected from the group consisting oflinear saturated C₁ to C₁₀ alkyl, linear unsaturated C₁ to C₁₀ alkyl,branched saturated C₁ to C₁₀ alkyl, branched unsaturated C₁ to C₁₀ alkyland C₇ to C₁₂ arylalkyl. Even more preferably the residues R¹ are equalto or different from each other, more preferably equal, and are selectedfrom the group consisting of linear saturated C₁ to C₆ alkyl, linearunsaturated C₁ to C₆ alkyl, branched saturated C₁ to C₆ alkyl, branchedunsaturated C₁ to C₆ alkyl and C₇ to C₁₀ arylalkyl. Yet more preferablythe residues R¹ are equal to or different from each other, morepreferably equal, and are selected from the group consisting of linearor branched C₁ to C₄ hydrocarbyl, such as for example methyl or ethyl.

Preferably the residues R² to R⁶ are equal to or different from eachother and linear saturated C₁ to C₄ alkyl or branched saturated C₁ to C₄alkyl. Even more preferably the residues R² to R⁶ are equal to ordifferent from each other, more preferably equal, and are selected fromthe group consisting of methyl, ethyl, iso-propyl and tert-butyl.

Preferably R⁷ and R⁸ are equal to or different from each other and areselected from hydrogen and methyl, or they are part of a 5-methylenering including the two indenyl ring carbons to which they are attached.In another preferred embodiment, R⁷ is selected from OCH₃ and OC₂H₅, andR⁸ is tert-butyl.

In a preferred embodiment the transition metal compound israc-methyl(cyclohexyl)silanediylbis(2-methyl-4-(4-tert-butylphenyl)indenyl)zirconiumdichloride.

In a second preferred embodiment, the transition metal compound israc-dimethylsilanediylbis(2-methyl-4-phenyl-1,5,6,7-tetrahydro-s-indacen-1-yl)zirconiumdichloride.

In a third preferred embodiment, the transition metal compound israc-dimethylsilanediylbis(2-methyl-4-phenyl-5-methoxy-6-tert-butylindenyl)zirconiumdichloride.

As a further requirement the solid catalyst system (SCS) according tothis invention must comprise a cocatalyst (Co) comprising an element (E)of group 13 of the periodic table (IUPAC), for instance the cocatalyst(Co) comprises a compound of Al.

Examples of such cocatalyst (Co) are organo aluminium compounds, such asaluminoxane compounds.

Such compounds of Al, preferably aluminoxanes, can be used as the onlycompound in the cocatalyst (Co) or together with other cocatalystcompound(s). Thus besides or in addition to the compounds of Al, i.e.the aluminoxanes, other cation complex forming cocatalyst compounds,like boron compounds can be used. Said cocatalysts are commerciallyavailable or can be prepared according to the prior art literature.Preferably however in the manufacture of the solid catalyst system onlycompounds of Al as cocatalyst (Co) are employed.

In particular preferred cocatalysts (Co) are the aluminoxanes, inparticular the C1 to C10-alkylaluminoxanes, most particularlymethylaluminoxane (MAO).

Preferably, the organo-zirconium compound of formula (I) and thecocatalyst (Co) of the solid catalyst system (SCS) represent at least 70wt %, more preferably at least 80 wt %, even more preferably at least 90wt %, even further preferably at least 95 wt % of the solid catalystsystem. Thus it is appreciated that the solid catalyst system isfeatured by the fact that it is self-supported, i.e. it does notcomprise any catalytically inert support material, like for instancesilica, alumina or MgCl₂ or porous polymeric material, which isotherwise commonly used in heterogeneous catalyst systems, i.e. thecatalyst is not supported on external support or carrier material. As aconsequence of that the solid catalyst system (SCS) is self-supportedand it has a rather low surface area.

In one embodiment the solid metallocene catalyst system (SCS) isobtained by the emulsion solidification technology, the basic principlesof which are described in WO 03/051934. This document is herewithincluded in its entirety by reference.

Hence the solid catalyst system (SCS) is preferably in the form of solidcatalyst particles, obtainable by a process comprising the steps of

-   a) preparing a solution of one or more catalyst components;-   b) dispersing said solution in a second solvent to form an emulsion    in which said one or more catalyst components are present in the    droplets of the dispersed phase,-   c) solidifying said dispersed phase to convert said droplets to    solid particles and optionally recovering said particles to obtain    said catalyst.

Preferably a first solvent, more preferably a first organic solvent, isused to form said solution. Still more preferably the organic solvent isselected from the group consisting of a linear alkane, cyclic alkane,aromatic hydrocarbon and halogen-containing hydrocarbon.

Moreover the second solvent forming the continuous phase is an inertsolvent towards to catalyst components, The second solvent might beimmiscible towards the solution of the catalyst components at leastunder the conditions (like temperature) during the dispersing step. Theterm “immiscible with the catalyst solution” means that the secondsolvent (continuous phase) is fully immiscible or partly immiscible i.e.not fully miscible with the dispersed phase solution.

Preferably the immiscible solvent comprises a fluorinated organicsolvent and/or a functionalized derivative thereof, still morepreferably the immiscible solvent comprises a semi-, highly- orperfluorinated hydrocarbon and/or a functionalized derivative thereof.It is in particular preferred, that said immiscible solvent comprises aperfluorohydrocarbon or a functionalized derivative thereof, preferablyC₃-C₃₀ perfluoroalkanes, -alkenes or -cycloalkanes, more preferredC₄-C₁₀ perfluoro-alkanes, -alkenes or -cycloalkanes, particularlypreferred perfluorohexane, perfluoroheptane, perfluorooctane orperfluoro(methylcyclohexane) or perfluoro (1,3-dimethylcyclohexane) or amixture thereof.

Furthermore it is preferred that the emulsion comprising said continuousphase and said dispersed phase is a bi- or multiphasic system as knownin the art. An emulsifier may be used for forming and stabilising theemulsion. After the formation of the emulsion system, said catalyst isformed in situ from catalyst components in said solution.

In principle, the emulsifying agent may be any suitable agent whichcontributes to the formation and/or stabilization of the emulsion andwhich does not have any adverse effect on the catalytic activity of thecatalyst. The emulsifying agent may e.g. be a surfactant based onhydrocarbons optionally interrupted with (a) heteroatom(s), preferablyhalogenated hydrocarbons optionally having a functional group,preferably semi-, highly- or perfluorinated hydrocarbons as known in theart. Alternatively, the emulsifying agent may be prepared during theemulsion preparation, e.g. by reacting a surfactant precursor with acompound of the catalyst solution. Said surfactant precursor may be ahalogenated hydrocarbon with at least one functional group, e.g. ahighly fluorinated C_(1-n) (suitably C₄₋₃₀ or C₅₋₁₅) alcohol (e.g.highly fluorinated heptanol, octanol or nonanol), oxide (e.g.propenoxide) or acrylate ester which reacts e.g. with a cocatalystcomponent, such as aluminoxane to form the “actual” surfactant.

In principle any solidification method can be used for forming the solidparticles from the dispersed droplets. According to one preferableembodiment the solidification is effected by a temperature changetreatment. Hence the emulsion subjected to gradual temperature change ofup to 10° C./min, preferably 0.5 to 6° C./min and more preferably 1 to5° C./min. Even more preferred the emulsion is subjected to atemperature change of more than 40° C., preferably more than 50° C.within less than 10 seconds, preferably less than 6 seconds.

For further details, embodiments and examples of the continuous anddispersed phase system, emulsion formation method, emulsifying agent andsolidification methods reference is made e.g. to the above citedinternational patent application WO 03/051934.

All or part of the preparation steps can be done in a continuous mannerReference is made to WO 2006/069733 describing principles of suchcontinuous or semicontinuous preparation methods of the solid catalysttypes, prepared via emulsion/solidification method.

The above described catalyst components are prepared according to themethods described in WO 01/48034.

The multi-layer biaxially oriented polymer film of the instant inventionis obtained by coextruding the core layer (CL) on the one side with apropylene copolymer composition (P) obtaining the sealing layer (SL).Optionally on the other side of the core layer (CL) an outer layer (OL),a second sealing layer (SL) or a metal layer (ML) can be placed. Thesecond sealing layer (SL) is preferably made also from a propylenecopolymer composition (P) according to this invention. Concerning theouter layer (OL) reference is made to the information provided above.

The layered structure of the multi-layer biaxially oriented polymer filmof the invention is formed by blown film extrusion, more preferably byblown film coextrusion processes, or by cast film extrusion, morepreferably by cast film coextrusion processes.

In case the multi-layer biaxially oriented polymer film is produced byblown film coextrusion the polymer melts of the polymer for the corelayer (CL), of the propylene copolymer composition (P) for the sealinglayer (SL) and optionally of the polymer for the outer layer (OL) or fora further sealing layer (SL) are extruded through an annular die andextruded into an unoriented heavy-wall tubular bubble which is watercooled and collapsed between nip rollers. Subsequently the tubular filmis preheated (130 to 160° C.) and blown into an oriented tubular bubblewhich is again collapsed between nip rollers and cooled. The blow upratio for the second bubble should generally be in the range of from 1.5to 5, such as from 2 to 4, preferably 2.5 to 3.5. Subsequently the metallayer (ML) is applied, if present.

In case the multi-layer biaxially oriented polymer film is produced bycast film technology the molten polymers are extruded through flatextrusion die onto a chill roll to cool the polymer to a solid film ofat least two layers. For the production of the multi-layer biaxiallyoriented polymer film the process is carried out by coextruding themelts of the polymer for the core layer (CL), of the propylene copolymercomposition (P) for the sealing layer (SL) and optionally of the polymerfor the outer layer (OL) or for a further sealing layer (SL),corresponding to the individual layers of the multi-layer biaxiallyoriented polymer film through flat-film multilayer die, taking off theresultant polymer film over one or more rolls for solidification. As itis conventional in the coextrusion process, the polymer of eachrespective individual layer is firstly compressed and liquefied in anextruder, it being possible for any additives to be already added to thepolymer or introduced at this stage via a masterbatch. The melts arethen forced simultaneously through a flat-film die (slot die), and theextruded multi-layer polymer film is taken off on one or more take-offrolls, during which it cools and solidifies. It has proven particularlyfavorable to keep the take-off roll or rolls, by means of which theextruded film is cooled and solidified, at a temperature from 10 to 50°C., preferably from 150 to 40° C. Orientation may be accomplished bystretching or pulling the film first in the machine direction (MD)followed by transverse direction (TD) orientation, like in thetenter-frame orientation process. Orientation may be sequential orsimultaneous, depending upon the desired film features. Preferredorientation ratios are commonly from between three to six in the machinedirection and between four to ten in the transverse direction.Subsequently the metal layer (ML) is applied, if present.

Optionally one or both, surface (s) of the multi-layer biaxiallyoriented polymer film can be corona- or flame-treated by one of theknown methods. For the corona treatment, the film is passed between twoconductor elements serving as electrodes, with such a high voltage,usually an alternating voltage (about 10000 V and 10000 Hz), beingapplied between the electrodes that spray or corona discharges canoccur. Due to the spray or corona discharge, the air above the filmsurface is ionized and reacts with the molecules of the film surface,causing formation of polar inclusions in the essentially non-polarpolymer matrix. The treatment intensities are in the usual range,preferably from 38 to 45 dynes/cm after production.

Furthermore the present invention is also directed to the use of theinventive multi-layer biaxially oriented polymer film as packingmaterial, in particular as a packing material for food and/or non-foodproducts like textiles, flowers, carton boxes containing tobacco productor perfumes.

In the following, the present invention is described by way of examples.

EXAMPLES

A. Measuring Methods

The following definitions of terms and determination methods apply forthe above general description of the invention as well as to the belowexamples unless otherwise defined.

Quantification of Microstructure by NMR Spectroscopy

Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used toquantify the isotacticity, regio-regularity and comonomer content of thepolymers.

Quantitative ¹³C {¹H} NMR spectra recorded in the molten-state using aBruker Advance III 500 NMR spectrometer operating at 500.13 and 125.76MHz for ¹H and ¹³C respectively. All spectra were recorded using a ¹³Coptimised 7 mm magic-angle spinning (MAS) probehead at 180° C. usingnitrogen gas for all pneumatics. Approximately 200 mg of material waspacked into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz.Standard single-pulse excitation was employed utilising the NOE at shortrecycle delays (as described in Pollard, M., Klimke, K., Graf, R.,Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W.,Macromolecules 2004, 37, 813, and in Klimke, K., Parkinson, M., Piel,C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys.2006, 207, 382) and the RS-HEPT decoupling scheme (as described inFilip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239, and inGriffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P.,Mag. Res. in Chem. 2007, 45, S1, S198). A total of 1024 (1 k) transientswere acquired per spectra.

Quantitative ¹³C {¹H} NMR spectra were processed, integrated andrelevant quantitative properties determined from the integrals. Allchemical shifts are internally referenced to the methyl isotactic pentad(mmmm) at 21.85 ppm.

The tacticity distribution was quantified through integration of themethyl region in the ¹³C {¹H} spectra, correcting for any signal notrelated to the primary (1,2) inserted propene stereo sequences, asdescribed in Busico, V., Cipullo, R., Prog. Polym. Sci. 2001, 26, 443and in Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L.,Macromolecules 1997, 30, 6251.

Characteristic signals corresponding to regio defects were observed(Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000,100, 1253). The influence of regio defects on the quantification of thetacticity distribution was corrected for by subtraction ofrepresentative regio defect integrals from specific integrals of thestereo sequences.

The isotacticity was determined at the triad level and reported as thepercentage of isotactic triad mm with respect to all triad sequences:% mm=(mm/(mm+mr+rr))*100

Characteristic signals corresponding to the incorporation of 1-hexenewere observed, and the 1-hexene content was calculated as the molepercent of 1-hexene in the polymer, H (mol %), according to:[H]=H _(tot)/(P _(tot) +H _(tot))where:H _(tot) =I(αB ₄)/2+I(ααB ₄)×2where I(α B₄) is the integral of the α B₄ sites at 44.1 ppm, whichidentifies the isolated 1-hexene incorporated in PPHPP sequences, andI(ααB₄) is the integral of the ααB₄ sites at 41.6 ppm, which identifiesthe consecutively incorporated 1-hexene in PPHHPP sequences.P_(tot)=Integral of all CH3 areas on the methyl region with correctionapplied for underestimation of other propene units not accounted for inthis region and overestimation due to other sites found in this region.and H(mol %)=100×[H]which is then converted into wt % using the correlationH(wt %)=(100×H mol %×84.16)/(H mol %×84.16+(100−H mol %)×42.08)

A statistical distribution is suggested from the relationship betweenthe content of hexene present in isolated (PPHPP) and consecutive(PPHHPP) incorporated comonomer sequences:[HH]<[H] ²

Calculation of comonomer content of the propylene copolymer (B):

$\frac{{C(P)} - {{w(A)}{{xC}(A)}}}{w(B)} = {C(B)}$wherein

-   w(A) is the weight fraction of the polypropylene (A),-   w(B) is the weight fraction of the propylene copolymer (B),-   C(A) is the comonomer content [in wt.-%] measured by ¹³C NMR    spectroscopy of the polypropylene (A), i.e. of the product of the    first reactor (R1),-   C(P) is the comonomer content [in wt.-%] measured by ¹³C NMR    spectroscopy of the propylene copolymer composition (P),-   C(B) is the calculated comonomer content [in wt.-%] of the the    propylene copolymer (B)    Mw, Mn, MWD

Mw/Mn/MWD are measured by Gel Permeation Chromatography (GPC) accordingto the following method:

The weight average molecular weight (Mw), the number average molecularweight (Mn), and the molecular weight distribution (MWD=Mw/Mn) ismeasured by a method based on ISO 16014-1:2003 and ISO 16014-4:2003. AWaters Alliance GPCV 2000 instrument, equipped with refractive indexdetector and online viscosimeter is used with 3×TSK-gel columns(GMHXL-HT) from TosoHaas and 1,2,4-trichlorobenzene (TCB, stabilizedwith 200 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 145° C.and at a constant flow rate of 1 mL/min. 216.5 μL of sample solution areinjected per analysis. The column set is calibrated using relativecalibration with 19 narrow MWD polystyrene (PS) standards in the rangeof 0.5 kg/mol to 11 500 kg/mol and a set of well characterized broadpolypropylene standards. All samples are prepared by dissolving 5 to 10mg of polymer in 10 mL (at 160° C.) of stabilized TCB (same as mobilephase) and keeping for 3 hours with continuous shaking prior sampling ininto the GPC instrument.

Melt Flow Rate (MFR)

The melt flow rates are measured with a load of 2.16 kg (MFR₂) at 230°C. The melt flow rate is that quantity of polymer in grams which thetest apparatus standardised to ISO 1133 extrudes within 10 minutes at atemperature of 230° C. under a load of 2.16 kg. Calculation of melt flowrate MFR₂ (230° C.) of the propylene copolymer (B):

${M\; F\;{R(B)}} = 10^{\lbrack\frac{{\log{({{MFR}{(P)}})}} - {{w{(A)}} \times {\log{({M\; F\;{R{(A)}}})}}}}{w{(B)}}\rbrack}$wherein

-   w(A) is the weight fraction of the polypropylene (A),-   w(B) is the weight fraction of the propylene copolymer (B),-   MFR(A) is the melt flow rate MFR₂ (230° C.) [in g/10 min] measured    according ISO 1133 of the polypropylene (A),-   MFR(P) is the melt flow rate MFR₂ (230° C.) [in g/10 min] measured    according ISO 1133 of the propylene copolymer composition (P),-   MFR(B) is the calculated melt flow rate MFR₂ (230° C.) [in g/10 min]    of the propylene copolymer (B).    Xylene Cold Soluble Fraction (XCS wt %)

Content of xylene cold solubles (XCS) is determined at 25° C. accordingISO 16152; first edition; 2005 Jul. 1.

Hexane Solubles

FDA section 177.1520

1 g of a polymer film of 100 μm thickness is added to 400 ml hexane at50° C. for 2 hours while stirring with a reflux cooler.

After 2 hours the mixture is immediately filtered on a filter paper No.41.

The precipitate is collected in an aluminium recipient and the residualhexane is evaporated on a steam bath under N₂ flow.

The amount of hexane solubles is determined by the formula((wt. sample+wt. crucible)−(wt crucible))/(wt. sample)·100.

Melting temperature T_(m), crystallization temperature T_(c), ismeasured with Mettler TA820 differential scanning calorimetry (DSC) on5-10 mg samples. Both crystallization and melting curves were obtainedduring 10° C./min cooling and heating scans between 30° C. and 225° C.Melting and crystallization temperatures were taken as the peaks ofendotherms and exotherms.

Also the melt- and crystallization enthalpy (Hm and Hc) were measured bythe DSC method according to ISO 11357-3.

Porosity: BET with N₂ gas, ASTM 4641, apparatus Micromeritics Tristar3000; sample preparation: at a temperature of 50° C., 6 hours in vacuum.

Surface area: BET with N₂ gas ASTM D 3663, apparatus MicromeriticsTristar 3000: sample preparation at a temperature of 50° C., 6 hours invacuum.

Mean particle size is measured with Coulter Counter LS200 at roomtemperature with n-heptane as medium; particle sizes below 100 nm bytransmission electron microscopy

Sealing Initiation Temperature (SIT); Sealing End Temperature (SET),Sealing Range:

The method determines the sealing temperature range (sealing range) ofpolymer films. The sealing temperature range is the temperature range,in which the films can be sealed according to conditions given below.

The lower limit (heat sealing initiation temperature (SIT)) is thesealing temperature at which a sealing strength of >1 N is achieved. Theupper limit (sealing end temperature (SET)) is reached, when the filmsstick to the sealing device.

The sealing range is determined on a DTC Hot tack tester Model 52-F/201with a film of 25 μm thickness with the following further parameters:

Specimen width: 25 mm

Seal Pressure: 0.66 N/mm²

Seal Time: 1 sec

Cool time: 30 sec

Peel Speed: 42 mm/sec

Start temperature: 80° C.

End temperature: 150° C.

Specimen is sealed sealing layer (SL) to sealing layer (SL) at eachsealbar temperature and seal strength (force) is determined at eachstep. All values of the SIT and SET were measured on the multi-layerfilm, like the three layer film as used in the examples. In cases wherethe SIT and SET refer to the propylene copolymer composition (P) or thesealing layer (SL) as such the SIT and SET were measured on a monolayercast film of the propylene copolymer composition (P) and the sealinglayer (SL), respectively, having a thickness of 100 μm as described inapplication No. 10 160 631.7. and application No. 10 160 611.9. SealingStrength is the force measured at the temperature defined in Table 2.

Hot Tack Force:

The hot tack force is determined on a DTC Hot tack tester Model 52-F/201with a film of 25 μm thickness with the following further parameters:

Specimen width: 25 mm

Seal Pressure: 1.2 N/mm²

Seal Time: 0.5 sec

Cool time: 0.2 sec

Peel Speed: 200 mm/sec

Start temperature: 90° C.

End temperature: 140° C.

The maximum hot tack force, i.e the maximum of a force/temperaturediagram is determined and reported.

Hot tack initiation temperature: is determined from the hot tack curveat the point where the force exceeds 1 N

Gloss was determined on the multi-layered films according to DIN67530-1982 at an angle of 20°.

Transparency, haze and clarity were determined on the multi-layeredfilms according to ASTM D1003-00

B. Examples

The propylene copolymer compositions (P) of table 1 have been producedin a Borstar PP pilot plant in a two-step polymerization processstarting in a bulk-phase loop reactor followed by polymerization in agas phase reactor, varying the molecular weight as well as hexenecontent by appropriate hydrogen and comonomer feeds. The catalyst usedin the polymerization process was a metallocene catalyst as described inexample 10 of WO 2010/052263 A1.

TABLE 1 Preparation of the propylene copolymer composition (P) P1 P2 P3Loop MFR₂ [g/10 min] 4.6 3.4 4.0 C6 [wt.-%] 0.0 1.2 1.2 XCS [wt.-%] <1.5<1.5 <1.5 GPR C6 [wt.-%] 5.5 5.9 7.4 Split Loop/GPR [%] 39/61 47/5345/55 FINAL C6 [wt.-%] 3.2 3.6 4.4 XCS [wt.-%] 2 2.3 5.5 HHS [wt.-%] 0.70.8 0.9 MFR₂ [g/10 min] 8.6 8.2 7.9 Mw [kg/mol] 226 224 210 MWD [−] 3.02.9 2.9 SIT [° C.] nm nm 102 Tm [° C.] 148 141 141 Tc [° C.] 111 97 100

-   Loop defines the polypropylene (A)-   GPR defines the propylene copolymer (B)-   Final defines the propylene copolymer (P)-   C6 is 1-hexene content-   HHS hexane hot soluble-   SIT Sealing initiation temperature measured on a monolayer film [100    μm] as described in application No. 10 160 631.7. and application    No. 10 160 611.9-   nm not measured-   P4 is the commercial propylene-ethylene-1-butene terpolymer TD210BF    of Borealis AG having a melt flow rate MFR₂ (230° C.) of 6 g/10 min,    a melting temperature Tm of 131° C. and a MWD of 4.9-   H-PP is the commercial polypropylene homopolymer HC101BF of Borealis    AG having a melt flow rate MFR₂ (230° C.) of 3.2 g/10 min, a melting    temperature Tm of 161° C.

Three layer biaxial oriented polymer films were produced on a BOPP pilotline. In the first step a three layer cast film was co-extruded by aflat t-shaped die with a die width of 300 mm. The film thickness of theco-extruded film was in the range of 800 μm to 900 μm. The melttemperature of the core layer (H-PP) was in the range of 255° C. to 260°C. The melt temperature of the sealing layer and the opposite layer(same polymer as the sealing layer) was in the range of 260° C. to 265°C. The produced three layer film was casted on a chill roll and cooledby a water bath with a temperature of 19° C. to 22° C. The temperatureof the chill roll was in the range of 23° C. to 24° C. The contact ofthe co-extruded film to the chill roll was supported by an air knifewith an air temperature of 35° C. to 39° C.

In a second step the casted film was longitudinal stretched by two pairsof temperature controlled rolls at a temperature at 109° C. to 111° C.The total stretching ratio in machine direction was 1:4.5. Afterwardsthe film was stretched in transverse direction in a tenter withmechanical clips at temperature higher as 150° C. Typical temperature inthe stretching zone of the tenter was 165° C. to 170° C. The stretchingratio of the three layer film in traverse direction was 1:8.0. In afurther zone the film was relaxed to a stretching ratio of 1:7.5 attemperature of 144° C. to 147° C. The final film sped was 63 m/min.

Afterwards the opposite layer to the sealing layer was corona treatedfor identification of the sealing layer at the following film testing.

In the final film structure of the produced three layer BOPP film thesealing layer and the opposite corona treated layer each had a thicknessof 0.5 μm to 1.8 μm (see table 2) and the thickness of the core layerwas 22 μm to 24 μm. The thickness of the three layers was controlled bythe throughput of the three corresponding extruders.

For the core layer (CL) H-PP has been used, whereas for the sealinglayers (SL) one of the polymers P1 to P4 have been used.

TABLE 2 Properties of the multi-layer biaxially oriented polymer filmCE1 CE2 IE1A IE1B IE2A IE2B IE3A IE3B P4 P4 P1 P1 P2 P2 P3 P3 LT [μm]1.2 0.5 1.5 0.6 1.4 0.7 1.8 0.7 HTF [N] 3.6 3.2 4.0 4.0 n.a. n.a. 6.24.0 HT-IT [° C.] 98 102 93 94 n.a. n.a. 85 88 SS (A) [N] 1.6 1.6 1.6 1.61.5 2.5 6.8 4.7 SS (B) [N] 3.3 3.0 3.9 3.6 3.9 6.3 9.2 5.4 SIT [° C.]110 110 110 110 110 105 100 100 T [%] 93.7 93.7 93.7 93.7 93.7 93.7 93.893.7 H [%] 1.1 0.9 0.6 0.6 0.8 0.5 0.9 0.4 C [%] 97.6 98.2 97.4 98.297.1 98.2 97.7 98.2

-   LT Layer thickness of the sealing layers determined by Scanning    Electron Microscopy-   SIT is the heat sealing initiation temperature-   HTF is the hot tack force-   HT-IT Hot Tack initiation temperature at F>1N (see page 32)-   SS(A) is the sealing strength at 105° C.-   SS(B) is the sealing strength at 110° C.-   T Transparency-   H Haze-   C Clarity

The invention claimed is:
 1. A multi-layer biaxially oriented polymerfilm comprising: (a) a core layer (CL) selected from the groupconsisting of polyvinyl alcohols, polyacrylates, polyamides,poly(ethylene terephthalate), polyolefins (PO) and mixtures thereof, and(b) a sealing layer (SL), said sealing layer (SL) comprises a propylenecopolymer composition (P), said propylene copolymer composition (P) (c1)has a comonomer content in the range of 3.0 to 8.0 wt. %, the comonomeris C₆ alpha olefin, (c2) comprises a polypropylene (A) and a propylenecopolymer (B) in the weight ratio [(A)/(B)] of 35/65 to 50/50, whereinsaid polypropylene (A) is a propylene homopolymer (H-A) or a propylenecopolymer (C-A) having a comonomer content of below 4.0 wt. %, thecomonomer is C₆ alpha olefin, and said propylene copolymer (B) has acomonomer content of 4.0 to 20.0 wt. %, the comonomer is C₆ alphaolefin, (c3) fulfills the ratio:MFR(A)/MFR(P)≤1.0 wherein MFR (A) is the melt flow rate MFR₂ (230° C.)[g/10 min] measured according to ISO 1133 of the polypropylene (A), MFR(P) is the melt flow rate MFR₂ (230° C.) [g/10 min] measured accordingto ISO 1133 of the propylene copolymer composition (P); (c4) has amelting temperature Tm determined by differential scanning calorimetry(DSC) of at least 135° C.; and (c5) has a heat sealing initiationtemperature (SIT) of equal or below 115° C.; and (c6) has a xylenesoluble content (XCS) determined at 25° C. according to ISO 16152 ofbelow 20.0 wt. %; and (c7) is free of any elastomeric component.
 2. Amulti-layer biaxially oriented polymer film according to claim 1,wherein the sealing layer (SL) and/or the propylene copolymercomposition (P) has/have a melt flow rate MFR₂ (230° C.) measuredaccording to ISO 1133 in the range of 2.0 to 50.0 g/10 min.
 3. Amulti-layer biaxially oriented polymer film according to claim 1,wherein the sealing layer (SL) and/or the propylene copolymercomposition (P) has/have: a molecular weight distribution (MWD) measuredby gel permeation chromatography (GPC) of at least 2.5.
 4. A multi-layerbiaxially oriented polymer film according to claim 1, wherein: (a) thecomonomer content in the polypropylene (A) is lower compared to thecomonomer content in the propylene copolymer (B), and/or (b) com (P)−com(A) is at least 1.0, wherein com (A) is the comonomer content of thepolypropylene (A) given in weight percent [wt. %], com (P) is thecomonomer content of the propylene copolymer composition (P) given inweight percent [wt. %].
 5. A multi-layer biaxially oriented polymer filmaccording to claim 1, wherein the sealing layer (SL) and/or thepropylene copolymer composition (P) fulfill(s) the equation (I):Tm−SIT≥22° C.  (I) wherein Tm is the melting temperature of the sealinglayer (SL) and/or of the propylene copolymer composition (P) determinedby differential scanning calorimetry (DSC) and given in centigrade [°C.], SIT is the heat sealing initiation temperature (SIT) given incentigrade [° C.] of the sealing layer (SL) and/or of the propylenecopolymer composition (P).
 6. A multi-layer biaxially oriented polymerfilm according to claim 1, wherein the polypropylene (A) of thepropylene copolymer composition (P): (a) is a propylene copolymer (C-A)with a comonomer content in the range of 0.5 to below 4.0 wt. %, and/or(b) has a melt flow rate MFR₂ (230° C.) measured according to ISO 1133of at least 1.5 g/10 min, and/or (c) has a xylene soluble content (XCS)of below 2.5 wt. %.
 7. A multi-layer biaxially oriented polymer filmaccording to claim 1, wherein said core layer (CL) comprises a propylenehomopolymer.
 8. A multi-layer biaxially oriented polymer film accordingto claim 1, wherein said core layer (CL) is a polypropylene (PP) or apropylene homopolymer (H-PP) having: (a) a melt flow rate MFR₂ (230° C.)measured according to ISO 1133 in the range of 1.0 to 15.0 g/10 min,and/or (b) a melting temperature Tm determined by differential scanningcalorimetry (DSC) of at least 155° C.
 9. A multi-layer biaxiallyoriented polymer film according to claim 1, wherein: (a) core layer (CL)has a thickness in the range of 5 to 80 μm, and/or (b) the sealing layer(SL) has a thickness in the range of 0.2 to 15 μm.
 10. A multi-layerbiaxially oriented polymer film according to claim 1, wherein saidmulti-layer biaxially oriented polymer film comprises three layers,namely the core layer (CL), the sealing layer (SL) and at least one of:(a) an outer layer (OL) being a polyolefin (PO), or (b) a furthersealing layer (SL), or (c) a metal layer (ML), wherein the multi-layerbiaxially oriented polymer film has the stacking order: (a1) sealinglayer (SL)-core layer (CL) outer layer (OL), or (b1) sealing layer(SL)-core layer (CL)-sealing layer (SL), or (c1) sealing layer (SL)-corelayer (CL)-a metal layer (ML).